A photoresist is applied to a substrate such as semiconductor wafer, glass, ceramic and metal to a thickness of from 0.5 to 2 .mu.m by a spin coating method or roller coating method. Thereafter, the coated material is heated, dried, exposed to radiation such as ultraviolet rays through an exposure mask to print a circuit pattern thereon, optionally followed by baking, and then developed to form an image thereon.
The coated mask is then etched with this image as a mask to effect a patternwise work on the substrate. Typical examples of fields to this technique is applied include process for the production of semiconductors such as IC and circuit boards for liquid crystal, thermal head, etc., and photofabrication process.
In the fine working of semiconductors using a photoresist, the prevention of reflection of light by the substrate has become more important as the dimensional fineness has developed. Heretofore, to this end, photoresists comprising a light absorber incorporated therein have been used. However, this approach is disadvantageous in that the resolving power is impaired. Therefore, the provision of a bottom anti-reflective coating (BARC) between the photoresist and the substrate has been widely studied.
As the anti-reflective coatings there have been known inorganic coatings made of titanium, titanium dioxide, titanium nitride, chromium oxide, carbon, .alpha.-silicone, etc. and organic coatings made of light absorber and polymer. The formation of the former coatings requires apparatus such as vacuum metallizer, CVD apparatus and sputtering apparatus while that of the latter coatings advantageously requires no special apparatus. Thus, the latter coatings have been widely studied.
Examples of the organic anti-reflective coatings include those comprising a condensate of diphenylamine derivative and formaldehyde-modified melamine resin, an alkali-soluble resin and a light absorber as described in JP-B-7-69611 (The term "JP-B" as used herein means an "examined Japanese patent publication"), those comprising a reaction product of maleic anhydride copolymer with diamine type light absorber as described in U.S. Pat. No. 5,294,680, those comprising a resin binder and a methylol melamine heat crosslinking agent as described in JP-A-6-118631 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), acrylic resin type anti-reflective coatings having a carboxylic acid group, an epoxy group and a light-absorbing group in the same molecule as described in JP-A-6-118656, and those comprising methylol melamine and a benzophenone light absorber as described in JP-A-8-87115.
The physical properties required for these organic anti-reflective coating materials are high absorbance with respect to radiation, insolubility in the resist solvent (no intermixing with the resist layer), higher dry etching rate than resist, etc. as described in Proc. SPIE, Vol. 2195, 225-229 (1994).
However, the compounds described in the above cited patents don't meet all of these requirements. Thus, improvements have been desired in this respect. For example, the prior art anti-reflective coatings leave something to be desired in the light absorbing capacity of binder and thus have needed a further light absorber to be incorporated therein. Further, the prevention of intermixing with the resist layer requires the introduction of heat crosslinking effect into the anti-reflective coating. Thus, the crosslinking effect has been introduced into the anti-reflective coating independently of the light absorbing group. Thus, this approach is disadvantageous in that if the crosslinkability of the anti-reflective coating is raised, the absorbance of the anti-reflective coating is reduced. Further, the anti-reflective coating comprising a functional group for enhancing alkali permeability such as carboxylic acid group as a crosslinking system are disadvantageous in that when developed with an aqueous solution of alkali, it is liable to swelling, impairing the shape of the resist pattern.